No, my opinions as expressed in this blog are not those of my employer. They're mine alone. That's why they're called "my opinions." Helloooo.

Wednesday, June 27, 2007

Value objects WTF!!?!!1!

Hmm. I just might try my hand at this "blogging" thing after all.

So here's something that has me really mystified about Java.

Let's say you want a simple class to represent a simple value object. Just a garden-variety thingamabob that has -- let's just say two fields. And these two fields together give the object its identity.

And you want this class of yours to be simple, basic, idiomatic and well-behaved.

This seems like a pretty common thing to want to do, right? So far so good?

Now, in my native language we have an expression for this situation, which loosely translates as, "what the mother****ing ****???"

What the hell happened? What did we do to deserve this? We just typed forty-four lines of code, not counting any documentation, just to create a ****ing struct, for Christ's sake! And we even had helper methods to call on for everything we reasonably could, at that!

And we'll end up typing it again. And again, and again. Except that in each place in our whole system we discover this pattern, it will have been deviated from in some subtle way or another. Forgot to make it cloneable, Forgot to make it serializable, a typo in equals() -- and tell the truth now, have you never once made that most appalling error of forgetting to implement hashCode()? Really?

So, we'd better write unit tests for all these classes too, then.

Object-oriented languages are meant to save us from duplication. But what we have here is a bona fide disaster. Something has failed us. But what can we reasonably do about it?

27 comments:

Yes, I agree, this is ridiculous. I started writing an Eclipse plug-in to easily create value objects. Still, you're stuck with a large piece of code.

One possibility is writing a code generator, but that requires infrastructure.

At first I thought the problem wasn't huge, but the more I think about it, I really want to simplify the process of returning multiple values from a method, and I probably have tended to change my design to avoid returning value objects.

I really wish it was easier to simplify some of these language problems (e.g. simplify creating exceptions)

OK, this has been meandery, but I'm half-typing, half watching Grey's Anatomy.

All this just belies the poor state of java's type system. Why should everything extend Object?

What's so special about a hashCode? It's a silly hack to make things like collections and comparisons standardized.

Im curious as to what solution you have. Creating a domain-specific Base-object/interface is one Ive seen a lot (UGH). Another is helper utils/delegates (EQUALLY UGH). Mixins are a somewhat better solution but difficult in java to achieve.

I strongly doubt if it really cannot be made simpler in Java. After all, you can implement hashCode and equals generically in a superclass using reflection. Besides that, didn't we go too far with usage of getters/setters? Are they really needed for such a simple value object case? Without them a value class could be reduced to this:

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